The present invention relates to sensors and, more particularly, to a traffic sensor which senses the impact of a vehicle tire.
Traffic management has become an important issue as a result of the increasing numbers of vehicles on the roads and the limited roadways available to handle the traffic. In order to manage traffic, both short and long term traffic volume of all major arteries in congested regions must be known. When this data is available, traffic engineers can provide solutions by redirecting traffic and/or by expanding the roadway system.
The present invention utilizes the residual charge present in certain materials as the energy source for a sensor. Study of the residual charge effect has led to the use of this technology for the present invention. An understanding of the effect has also led to the design of a transmission cable for transmitting the sensed signals to recording equipment without corruption by cross-talk from neighboring sensors.
Evidence of a permanent residual charge has been observed in many insulating and semi-insulating materials, a result of the manufacturing process. This residual charge is employed in the present invention to generate a static electric field. Generation of the electric field is achieved with a first electrode, a first dielectric in intimate contact with the first electrode, and a second electrode separated from the first dielectric with a second dielectric. The electric field, combined with a mechanical force supplied by an object striking the sensor, such as a tire, generates a signal pulse.
The residual charge effect employed herein is separate and distinct from either ferroelectric or electret materials, wherein the molecular structure of the dielectric material is oriented in such a way as to effect polarization of the material. The present invention, by contrast, makes use of common materials and does not alter the molecular properties of the dielectric.